The present invention generally relates to power system monitoring, and more specifically, to a system and method for detecting power system conditions.
Electric utility systems or power systems are designed to generate, transmit and distribute electrical energy to loads via a variety of power system elements such as electrical generators, power transformers, power transmission lines, distribution lines, buses and capacitors, to name a few. As a result, power systems are typically monitored and protected using a number of different types of protective devices having associated protective schemes. Such protective schemes protect the power system elements from abnormal conditions such as electrical short circuits, overloads, power swings, pole slips, frequency excursions, voltage fluctuations, and the like.
In general, protective devices and their protective schemes act to isolate, or disconnect portions of the power system or power system element(s) (e.g., a generator, transformers, buses, motors, etc.) from the remainder of the power system upon detection of an abnormal condition or fault in one or more power system element(s). Such protective devices may include different types of protective relays, surge protectors, arc gaps and associated circuit breakers and reclosures.
Inadvertent disconnection of one or more portions of the power system however is undesirable. Such “islanding” may occur during excessive power flow conditions, transmission line maintenance, periods following damage to elements of the power system, etc. causing circuit breaker operation to isolate that portion of the power system from the remainder. As a result of islanding, power generation and loads may not balanced, thereby causing undesirable decreases or increases in the power system frequency, loss of available power for motor starting, or loss of coordination of the protective device, to name a few. At a minimum, islanding causes a loss of generation and load diversity and therefore reduces power system reliability. In cases where power system operators are unaware of the existence of one or more the power system “islands” or are unable to pin-point boundaries of the power system islands, they may not take appropriate corrective actions. Equipment damages, loss of generators and loads may follow.
The problem of islanding has been addressed using a variety of methods. One method includes viewing/monitoring power system frequency at various locations throughout the power system. Unfortunately, the direct use of power system frequency to determine an occurrence of islanding, or to pin-point islanding locations, is inherently slow and may therefore fail to detect the islanding before automatic or manual controls exacerbate the problem. In addition to its inherent speed problem, instruments used to view the power system frequency may not have the necessary response characteristic required to accurately depict the situation to the power system operator.